"The elucidation of molecular alterations that occur during human breast cancer development may permit the identification of preventative strategies for women at high risk. Lesions such as atypical ductal hyperplasia (ADH) and ductal carcinoma in situ (DCIS) confer 4- and 8-10 fold increases in risk for the development of invasive carcinoma, respectively. We examined a cohort of approximately 100 human biopsy specimens using in situ hybridization to examine trends in mRNA expression levels, with the goal of identifying genes whose expression patterns correlated with increasing risk. Two genes, cyclin D and the RXR form of the retinoic acid receptor superfamily, exhibited quantitatively increased mRNA levels in DCIS specimens than in normal ductal/lobular units in the margin of the specimen. Overexpression of these two genes therefore correlates with increased risk for development of invasive breast carcinoma. Cyclin D has been transfected into the human immortal MCF-10A breast cell line. Increased anchorage-independent, but not anchorage-dependent growth was observed. Interestingly, the anchorage-independent growth of cyclin D transfectants was several fold to a log more senstive to the inhibitory effects of g-irradiation than the control transfectants. This inhibition was accompanied by increased apoptosis, and could be replicated using the apoptosis inducer Apo-2, but not using TNF-a. We conclude that cyclin D overexpression can produce colonization-competent cells in the breast, and that certain apoptosis inducers may hold promise for eliminating such cells."